Sometimes used by extension for any confusing acronym. People
who like this looser usage argue that not all TLAs have three
letters, just as not all four-letter words have four letters.
One also hears of "ETLA" (Extended Three-Letter Acronym) being
used to describe four-letter acronyms. The term "SFLA"
(Stupid Four-Letter Acronym) has also been reported.

The self-effacing phrase "TDM TLA" (Too Damn Many...) is used to
bemoan the plethora of TLAs in use. In 1989, a random of the
journalistic persuasion asked hacker Paul Boutin "What do you
think will be the biggest problem in computing in the 90s?"
Paul's straight-faced response: "There are only 17,000
three-letter acronyms." (To be exact, there are 26^3 = 17,576.)